Direct and selective production of acetaldehyde from acetic acid utilizing a supported metal catalyst

ABSTRACT

A process for the selective production of acetaldehyde by vapor phase reaction of acetic acid over a hydrogenating catalyst composition to form acetaldehyde is disclosed and claimed. In an embodiment of this invention reaction of acetic acid and hydrogen over platinum and iron supported on silica selectively produces acetaldehyde in a vapor phase at a temperature of about 300° C.

FIELD OF THE INVENTION

The present invention relates generally to a process for the productionof acetaldehyde from acetic acid. More specifically, the presentinvention relates to a process including hydrogenating acetic acidutilizing a supported metal catalyst, such as, for example, iron,platinum or ruthenium supported on a suitable catalyst supportoptionally including one or more additional hydrogenating metals to formacetaldehyde with high selectivity.

BACKGROUND

There is a long felt need for an economically viable process to convertacetic acid to acetaldehyde. Acetaldehyde is an important commodityfeedstock for a variety of industrial products. For instance,acetaldehyde can readily be hydrogenated to ethanol, which in itself haswide variety of industrial applications including its wide utility as agasoline additive. Acetaldehyde can also be converted to ethyl acetateby the Tischenko reaction or reacted with other compounds to form otherproducts. Currently acetaldehyde is produced by the oxidation ofethylene, the Wacker oxidation of ethylene. Fluctuating natural gas andcrude oil prices contribute to fluctuations in the cost ofconventionally produced, petroleum or natural gas-sourced acetaldehyde,making the need for alternative sources of acetaldehyde all the greaterwhen oil prices rise. Thus it is of interest to develop commerciallyviable routes to selectively hydrogenate acetic acid to acetaldehyde.

The catalytic hydrogenation of aromatic carboxylic acids to producearomatic aldehydes has been reported in the literature. For instance,U.S. Pat. No. 4,613,700 to Maki et al. discloses that aromatic aldehydescan be formed from aromatic carboxylic acids using a catalyst comprisingzirconium oxide containing as an essential component at least oneelement selected from the group consisting of chromium, manganese, iron,cobalt, zinc, bismuth, lead rhenium and the elements of Group III inperiods 3 to 6 of the periodic table. However, no examples of catalytichydrogenation of aliphatic carboxylic acids such as acetic acid areprovided in this disclosure.

U.S. Pat. No. 5,306,845 to Yokohama et al. discloses a method lo ofproducing an aldehyde, which comprises hydrogenating a carboxylic acidor its alkyl ester with molecular hydrogen in the presence of a catalystcontaining chromium oxide of high purity having a specific surface areaof at least 10 m²/g and a total content of sodium, potassium, magnesiumand calcium of not more than 0.4 weight percent. It is further reportedtherein that the hydrogenation reaction is conducted while maintainingthe carboxylic acid or its alkyl ester at a concentration of not morethan 10 volume percent. Additionally, the only example reported thereinis hydrogenation of stearic acid to stearyl aldehyde. Most importantly,the selectivity to aldehyde drops significantly even if the totalcontent of sodium, potassium, magnesium and calcium increases from about0.3 weight percent to about 0.46 weight percent, thus rendering theprocess not suitable for a commercial operation.

U.S. Pat. No. 5,476,827 to Ferrero et al. describes a process for thepreparation of aldehydes by catalytic hydrogenation of carboxylic acids,esters or anhydrides utilizing a bimetallic ruthenium/tin catalyst. Thepreferred carboxylic acids are the α-β-unsaturated carboxylic acids withan aromatic back bone or aromatic carboxylic acids. No examples ofaliphatic carboxylic acids including acetic acid are provided.

U.S. Pat. No. 6,121,498 to Tustin et al. discloses a method forproducing acetaldehyde from acetic acid. In this process, acetic acid ishydrogenated with hydrogen at an elevated temperature in the presence ofan iron oxide catalyst containing between 2.5 and 90 weight percentpalladium. However, the optimal condition reported therein is comprisedof an iron oxide catalyst containing at least about 20 weight percentpalladium, which affords about 80 percent selectivity to acetaldehydewith about 50 percent conversion of acetic acid. Additionally,significant amounts of by-products including methane, ethane, ethylene,ethanol and acetone are formed.

From the foregoing it is apparent that existing processes do not havethe requisite catalysts to selectively convert acetic acid toacetaldehyde or existing art employs catalysts, which are eitherexpensive and/or non-selective for the formation of acetaldehyde andproduces undesirable by-products.

SUMMARY OF THE INVENTION

Surprisingly, it has now been unexpectedly found that acetaldehyde canbe made on an industrial scale directly from acetic acid with very highselectivity and yield. More particularly, this invention provides aprocess for the selective formation of acetaldehyde from acetic acidcomprising: hydrogenating acetic acid in the presence of hydrogen over ahydrogenating catalyst comprising at least one metal selected from thegroup consisting of iron, copper, gold, platinum, palladium andruthenium supported on a suitable catalyst support. Optionally, thecatalyst is further comprised of one or more metal catalysts selectedfrom the group consisting of tin, aluminum, potassium, cobalt,molybdenum, tungsten and vanadium. More specifically, the catalystsuitable for the process of this invention is typically comprised ofsupported ruthenium alone or in combination with tin or iron; asupported iron alone or in combination with platinum or cobalt; or acombination of platinum and tin. Similarly, other catalysts suitable inthe process of this invention include supported palladium alone or acombination of palladium/gold (Pd/Au) or palladium/copper (Pd/Cu), whichcan further comprise potassium acetate. Also suitable catalysts are acombination of palladium/iron (Pd/Fe), iron/cobalt (Fe/Co),copper/molybdenum (Cu/Mo) or copper/aluminum. Suitable catalyst supportsinclude without any limitation, silica, alumina, calcium silicate,carbon, zirconia, zirconia-silica, titania, titania-silica, iron oxideand zeolite catalysts such as for example H-ZSM-5. Silica and iron oxideare particularly preferred catalyst supports in the process of thisinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in detail below with reference to numerousembodiments for purposes of exemplification and illustration only.Modifications to particular embodiments within the spirit and scope ofthe present invention, set lo forth in the appended claims, will bereadily apparent to those of skill in the art.

Unless more specifically defined below, terminology as used herein isgiven its ordinary meaning.

Typically, the catalyst metal loadings are expressed as weight percentof a catalyst metal based on the total dry weight of the metal andcatalyst support. Thus, for example, one (1) weight percent of metal ona support means that one gram of pure metal is present in 100 grams ofsupported metal catalyst, i.e., the combined weight of support (99grams) and the metal (1 gram).

“Conversion” is expressed as a mole percentage based on acetic acid inthe feed. The conversion of acetic acid (AcOH) is calculated from gaschromatography (GC) data using the following equation:

${{AcOH}\mspace{14mu} {conversion}\mspace{11mu} (\%)} = {100*\frac{{{mmol}\mspace{14mu} {AcOH}\mspace{14mu} {in}\mspace{11mu} \left( {{feed}\mspace{14mu} {stream}} \right)} - {{mmol}\mspace{14mu} {AcOH}\mspace{14mu} {out}\mspace{11mu} ({GC})}}{{mmol}\mspace{14mu} {AcOH}\mspace{14mu} {in}\mspace{11mu} \left( {{feed}\mspace{14mu} {stream}} \right)}}$

“Selectivity” is expressed as a mole percent based on converted aceticacid. For example, if the conversion is 50 mole % and 50 mole % of theconverted acetic acid is converted to acetaldehyde (AcH), we refer tothe acetaldehyde selectivity as 50%. Selectivity is calculated from gaschromatography (GC) data using the following equation:

${{Selectivity}\mspace{14mu} {to}\mspace{14mu} {AcH}\mspace{11mu} (\%)} = {100*\frac{{mmol}\mspace{14mu} {AcH}\mspace{14mu} {out}\mspace{11mu} ({GC})}{\frac{{Total}\mspace{14mu} {mmol}\mspace{14mu} C\mspace{14mu} {out}\mspace{11mu} ({GC})}{2} - {{mmol}\mspace{14mu} {AcOH}\mspace{14mu} {out}\mspace{11mu} ({GC})}}}$

wherein “Total mmol C out (GC)” refers to total mmols of carbon from allof the products analyzed by gas chromatograph.

The reaction proceeds in accordance with the following chemicalequation:

In accordance with the invention, conversion of acetic acid toacetaldehyde can be carried out in a variety of configurations, such asfor example in a single reaction zone which may be a layered fixed bed,if so desired. An adiabatic reactor could be used, or a shell and tubereactor provided with a heat transfer medium could be used. The fixedbed can comprise a mixture of different catalyst particles or catalystparticles which include multiple catalysts as further described herein.The fixed bed may also include a layer of particulate material making upa mixing zone for the reactants. A reaction mixture including aceticacid, hydrogen and optionally an inert carrier gas is fed to the bed asa stream under pressure to the mixing zone. The stream is subsequentlysupplied (by way of pressure drop) to the reaction zone or layer.Reaction zone comprises a catalytic composition including a suitablehydrogenating catalyst where acetic acid is hydrogenated to produceacetaldehyde. Any suitable particle size may be used depending upon thetype of reactor, throughput requirements and so forth.

Although various metal supported hydrogenating catalysts known to oneskilled in the art can be employed in hydrogenating acetic acid to formacetaldehyde in the process of this invention it is preferred that thehydrogenating catalyst employed contains at least one or more metalsselected from the group consisting of iron, copper, gold, platinum,palladium and ruthenium supported on a suitable catalyst support.Optionally, a second or third metal can be selected from the groupconsisting of tin, aluminum, potassium, cobalt, molybdenum, tungsten andvanadium. Preferably, the catalyst suitable for the process of thisinvention is comprised of ruthenium alone, supported on a suitablesupport such as iron oxide or silica or a combination of ruthenium andtin or ruthenium and iron supported on a suitable catalyst support.Similarly, the preferred hydrogenation catalyst is iron alone supportedon a suitable support such as silica or a combination of iron andplatinum or a combination of iron and cobalt supported on a suitablecatalyst support such as silica. Similarly, other catalysts suitable inthe process of this invention include supported palladium alone or acombination of palladium/gold (Pd/Au) or palladium/copper (Pd/Cu), whichcan further comprise potassium acetate. Also suitable catalysts are acombination of palladium/iron (Pd/Fe), iron/cobalt (Fe/Co),copper/molybdenum (Cu/Mo) or copper/aluminum.

Typically, when bimetallic catalysts are employed it is preferred that asuitable weight ratio of a combination of metals on a suitable supportcan be used as a hydrogenating catalyst. Thus, for example, acombination of ruthenium and iron (Ru/Fe), ruthenium and tin (Ru/Sn),palladium/copper (Pd/Cu), palladium/iron (Pd/Fe) in the weight ratio ofabout 0.1-1 are particularly preferred. More preferably, a weight ratioof Ru/Fe or Ru/Sn or Pd/Cu or Pd/Fe is about 0.2-0.5 and most preferablythe weight ratio of Ru/Fe or Ru/Sn or Pd/Cu or Pd/Fe is about 0.2.Similar weight ratios can be employed for a catalyst combination ofplatinum and iron Pt/Fe, i.e., a weight ratio of 0.1-1, preferably0.2-0.5 and most preferably 0.2. When a combination of cobalt and iron(Co/Fe) or copper/molybdenum (Cu/Mo) or copper/aluminum (Cu/Al)supported on a suitable catalyst support is employed, the preferredweight ratio of Co/Fe or Cu/Mo or Cu/Al is in the range of 1 to 5. Forinstance, a combination of 17.4 weight percent of cobalt and 4.8 weightpercent of iron supported on silica is commercially available.Similarly, a copper-aluminum catalyst is sold under the name of T-4489by Sud Chemie.

When ruthenium alone or palladium alone or iron alone is used as themetal catalyst on a suitable support any loading level of ruthenium,palladium or iron can be employed so as to affect the selectivehydrogenation of acetic acid to acetaldehyde. Typically, however, theruthenium or palladium loading level can range from 0.5 weight percentto about 20 weight percent, preferably 1 weight percent to about 10weight percent and most preferably 1 weight percent to about 5 weightpercent. Generally when a noble metal such as ruthenium or palladiumalone are employed in the process of this invention, 0.5 to 1 weightpercent of catalyst metal may be sufficient to obtain the optimumcatalytic benefit. Preferred catalyst supports for ruthenium orpalladium are iron oxide or silica. Similarly, when iron alone is usedas the metal catalyst, the loading level of iron can range from I weightpercent to about 20 weight percent, preferably 2 weight percent to about10 weight percent and most preferably 3 weight percent to about 8 weightpercent. Preferred catalyst support for iron is silica.

When bimetallic catalysts employed are two noble metals such aspalladium and gold then the metal loading of each of the noble metalloading is in the range of from about 0.5 weight percent to about 20weight percent, preferably 1 weight percent to about 10 weight percentand most preferably 1 weight percent to about 5 weight percent. However,as already noted above, low loadings of about 0.5 weight percent or 1weight percent of each of the noble metals, such as palladium or goldbrings about optimum catalytic effect in the process of this invention.

Various catalyst supports known in the art can be used to support thecatalysts of this invention. Examples of such supports include withoutany limitation, zeolite, such as H-ZSM-5, iron oxide, silica, alumina,titania, zirconia, magnesium oxide, calcium silicate, carbon, graphiteand a mixture thereof. Preferred supports are silica and iron oxide.More preferably silica is used as a catalyst support in the process ofthis invention. It is also important to note that the higher the purityof silica, the better it is as a support. Various forms of commerciallyavailable silica supports can be used in this invention including highsurface area silica (HSA silica) as well as low surface area silica (LSAsilica).

In another aspect of the process of this invention, any of known zeolitecatalysts can also be employed as a catalyst support. While any zeolitehaving a pore diameter of at least about 0.6 nm can be used, preferablyemployed among such zeolites are the catalyst supports selected from thegroup consisting of mordenites, ZSM-5, a zeolite X and a zeolite Y.

The preparation of large-pore mordenites is described, for example, inU.S. Pat. No. 4,018,514 and in Mol. Sieves Pap. Conf., 1967, 78, Soc.Chem. Ind. London, by D. DOMINE and J. QUOBEX.

Zeolite X is described, for example, in U.S. Pat. No. 2,882,244 andzeolite Y in U.S. Pat. No. 3,130,007.

Various zeolites and zeolite-type materials are known in the art for thecatalysis of chemical reactions. For example, U.S. Pat. No. 3,702,886,of Argauer, discloses a class of synthetic zeolites, characterized as“Zeolite ZSM-5”, which are effective for the catalysis of varioushydrocarbon conversion processes.

The zeolites suitable for the procedure of the invention can be in thebasic form, in the partially or totally acidified form, or in thepartially dealuminated form.

Preferably, the zeolite catalyst support in the process of the presentinvention are in the protic form, characterized as “H-ZSM-5” or“H-mordenite” zeolites, which are prepared from a corresponding “ZSM-5”zeolite or “mordenite” zeolite by replacing most, and generally at leastabout 80% of the cations of the latter zeolite with hydrogen ions usingtechniques well-known in the art. These zeolite catalysts areessentially crystalline aluminosilicates or in the neutral form, acombination of silica and alumina in a well defined crystallinestructure. In a particularly preferred class of zeolite catalysts forpurposes of the present invention, the molar ratio of SiO₂ to Al₂O₃ inthese zeolites is within the ratio of about 10 to 60.

In another aspect of this invention, ruthenium is supported on eithersilica or iron oxide. A combination of ruthenium and tin, iron alone ora combination of platinum and iron, iron and cobalt, iron and ruthenium,and platinum and tin are supported on a high purity, low surface areasilica or high purity, high surface area silica using the procedureswell known in the art or the procedures further described herein. Otherpreferred catalyst supports for platinum or ruthenium based metalcatalysts are titania and zirconia.

As noted above, the loading levels of a combination of two metalcatalysts are generally referenced with the content of main catalystmetal and the weight ratio of the combination. For instance, the weightratio of Ru/Sn, Ru/Fe, Pt/Sn or Pt/Fe is in the range of about 0.1 to 2.Thus, when the weight ratio of Ru/Sn, Ru/Fe or Pt/Fe is 0.1, the amountof ruthenium or platinum can be 0.1 or 1 weight percent and thus 1 or 10weight percent of tin or iron is present on the catalyst support.Preferably, the weight ratio of Ru/Sn, Ru/Fe, Pt/Sn or Pt/Fe is about0.5, and thus the amount of ruthenium or platinum on the catalystsupport can be either 0.5 or 1 weight percent and that of tin or iron iseither one or two weight percent. More preferably, the weight ratio ofRu/Sn, Ru/Fe, Pt/Sn or Pt/Fe is one or 0.2. Thus the amount of rutheniumor platinum on a support is 0.5, one or two weight percent and that oftin or iron is also 0.5, one or two weight percent when the weight ratiois one. Similarly, when a weight ratio of Ru/Sn, Ru/Fe or Pt/Fe is 0.2,the amount of ruthenium or platinum on the support can be 0.5 or oneweight percent and of tin or iron is either 2.5 or five weight percent.

The amount of third metal loading if present on a support is not verycritical in this invention and can vary in the range of about 0.1 weightpercent to about 10 weight percent. A metal loading of about 1 weightpercent to about 6 weight percent based on the weight of the support isparticularly preferred.

The metal impregnation can be carried out using any of the known methodsin the art. Typically, before impregnation the supports are dried at120° C. and shaped to particles having size distribution in the range ofabout 0.2 to 0.4 mm. Optionally, the supports may be pressed, crushedand sieved to a desired size distribution. Any of the known methods toshape the support materials into desired size distribution can beemployed.

For supports having low surface area, such as, for example,alpha-alumina, the metal solutions are added in excess until completewetness or excess liquid impregnation so as to obtain desirable metalloadings.

As noted above, the hydrogenation catalysts used in the process of thisinvention are generally bimetallic containing platinum/iron,ruthenium/tin, ruthenium/iron, iron/cobalt and so on. Generally, withoutintending to be bound by any theory, it is believed that one metal actsas a promoter metal and another metal is the main metal. For instance,in the instant process of the invention, of the above noted combinationsrespectively, platinum, ruthenium, and iron are considered as mainmetals for preparing hydrogenation catalysts of this invention. Theother metals, tin with ruthenium and iron with cobalt, platinum orruthenium are considered to be the promoter metals depending uponvarious reaction parameters including, but not limited to catalystsupport employed, reaction temperature and pressure, etc. The catalystsmay include other promoter metals, such as tungsten, vanadium,molybdenum, chromium or zinc.

The bimetallic catalysts are generally impregnated in two steps. Eachimpregnation step is followed by drying and calcination. The bimetalliccatalysts may also be prepared by co-impregnation. In most cases, theimpregnation may be carried out using metal nitrate solutions. However,various other soluble salts which upon calcinations release metal ions,can also be used. Examples of other suitable metal salts forimpregnation include metal oxalate, metal hydroxide, metal oxide, metalacetate, ammonium metal oxide, such as ammonium heptamolybdatehexahydrate, metal acids, such as perrhenic acid solution, and the like.

Thus in one embodiment of this invention, there is provided ahydrogenation catalyst wherein the catalyst support is silica or ironoxide with ruthenium alone as the hydrogenation catalyst. In this aspectof the invention the metal loading of ruthenium can range from one (1)weight percent to about twenty (20) weight percent, preferably one toten weight percent and most preferably one to five weight percent.

In another embodiment of this invention, there is provided ahydrogenation catalyst wherein the catalyst support is silica with ironalone as the hydrogenation catalyst. In this aspect of the invention themetal loading of iron can range from one (1) weight percent to abouttwenty (20) weight percent, preferably two to ten weight percent andmost preferably three to eight weight percent of iron.

In another embodiment of this invention, there is provided a bimetallicloading of ruthenium and tin or platinum and tin. In this aspect of theinvention, the loading of ruthenium or platinum is about 0.5 weightpercent to about 2 weight percent and the loading of tin is about 2.5weight percent to about 10 weight percent. Specifically, ruthenium/tinor platinum/tin loading levels of 1/1, 1/5, 0.5/5, and 0.5/2.5 weightpercent on silica can be used.

In another embodiment of this invention, there is further provided ahydrogenation catalyst wherein the catalyst support is high purity, lowsurface area silica with a bimetallic loading of platinum and iron orruthenium and iron. In this aspect of the invention, the loading ofplatinum or ruthenium is about 0.5 weight percent to about 2 weightpercent and the loading of iron is about 4 weight percent to about 10weight percent. Specifically, platinum/iron or ruthenium/iron loadinglevels of 1/1, 1/5, 0.5/5, and 0.5/2.5 weight percent on high purity,low surface area silica can be used. Other preferred supports in thisaspect of the invention include H-ZSM-5, graphitized carbon, zirconia,titania, iron oxide, silica-alumina and calcium silicate.

In another embodiment of this invention, there is further provided ahydrogenation catalyst wherein the bimetallic catalyst is cobalt andiron supported on silica. In this aspect of the invention, the loadinglevel of cobalt is about 12 weight percent to about 22 weight percentand of iron is from about 3 to 8 weight percent. Specifically, cobaltloading level of 17.4 weight percent and iron loading level of 4.8weight percent supported on silica is commercially available.

In general, by the practice of this invention, acetic acid canselectively be converted to acetaldehyde at very high rates. Theselectivity to acetaldehyde in general is very high and may be at least60 percent. Under preferred reaction conditions, acetic acid isconverted to acetaldehyde at a selectivity of at least 70 percent ormore preferably at a selectivity of over 80 percent such as at least 90percent.

The conversion of acetic acid using the catalysts of this invention isat least 10% and can be up to 40% with selectivity to acetaldehyde atleast 60%, preferably 70% and most preferably 80%.

Generally, the active catalysts of the invention are the single metal orthe bimetallic catalysts as described herein. More specifically, abimetallic catalyst containing ruthenium and tin, ruthenium and iron,platinum and tin, platinum and iron, and cobalt and iron supported onsilica with a ruthenium or platinum loadings of 0.5 to 1 weight percentand tin and iron loadings of 5 weight percent and cobalt loading ofabout 18 weight percent are preferred. In accordance with the practiceof this invention, acetic acid can be converted using this catalyst atconversions of around 40% with acetaldehyde selectivity of at least 60%,more preferably selectivity to acetaldehyde of at least 80% can beachieved.

Similar conversions and selectivities are achieved using zirconia,graphite or titania as a support and with similar loadings of ruthenium,platinum, tin, iron and cobalt as described above. Other promoter metalscan also be used in conjunction with ruthenium or platinum as notedabove.

In another aspect of this invention it is also possible to obtain highlevels of conversions in the order of at least 25% and high selectivityto acetaldehyde of at least about 80% using ruthenium or iron loading ofone weight percent to about five weight percent on silica or iron oxideas catalyst supports. In this aspect of the invention, other preferredcatalyst supports include graphitized carbon, titania, zirconia,silica-alumina and calcium silicate.

In another aspect of the process of this invention, the hydrogenation iscarried out at a pressure just sufficient to overcome the pressure dropacross the catalytic bed.

The reaction may be carried out in the vapor or liquid state under awide variety of conditions. Preferably, the reaction is carried out inthe vapor phase. Reaction temperatures may be employed, for example inthe range of about 250° C. to about 350° C., preferably about 290° C. toabout 310° C. The pressure is generally uncritical to the reaction andsubatmospheric, atmospheric or superatmospheric pressures may beemployed. In most cases, however, the pressure of the reaction will bein the range of about 5 to 30 atmospheres absolute, most preferably thepressure of reaction zone is in the range of about 8 to 20 atmospheresabsolute.

Although the reaction consumes a mole of hydrogen per mole of aceticacid to produce a mole of acetaldehyde, the actual molar ratio of aceticacid to hydrogen in the feed stream may be varied between wide limits,e.g. from about 100:1 to 1:100. It is preferred however, that such ratiobe in the range of about 1:20 to 1:2. More preferably, the molar ratioof acetic acid to hydrogen is about 1:5.

The raw materials used in connection with the process of this inventionmay be derived from any suitable source including natural gas,petroleum, coal, biomass and so forth. It is well known to produceacetic acid through methanol carbonylation, acetaldehyde oxidation,ethylene oxidation, oxidative fermentation, and anaerobic fermentationand so forth. As petroleum and natural gas have become more expensive,methods for producing acetic acid and intermediates such as methanol andcarbon monoxide from alternate carbon sources have drawn more interest.Of particular interest is the production of acetic acid from synthesisgas (syngas) that may be derived from any suitable carbon source. U.S.Pat. No. 6,232,352 to Vidalin, the disclosure of which is incorporatedherein by reference, for example, teaches a method of retrofitting amethanol plant for the manufacture of acetic acid. By retrofitting amethanol plant the large capital costs associated with CO generation fora new acetic acid plant are significantly reduced or largely eliminated.All or part of the syngas is diverted from the methanol synthesis loopand supplied to a separator unit to recover CO and hydrogen, which arethen used to produce acetic acid. In addition to acetic acid, theprocess can also be used to make hydrogen which is utilized inconnection with this invention.

U.S. Pat. No. RE 35,377 Steinberg et al., also incorporated herein byreference, provides a method for the production of methanol byconversion of carbonaceous materials such as oil, coal, natural gas andbiomass materials. The process includes hydrogasification of solidand/or liquid carbonaceous materials to obtain a process gas which issteam pyrolized with additional natural gas to form synthesis gas. Thesyngas is converted to methanol which may be carbonylated to aceticacid. The method likewise produces hydrogen which may be used inconnection with this invention as noted above. See also, U.S. Pat. No.5,821,111 Grady et al., which discloses a process for converting wastebiomass through gasification into synthesis gas as well as U.S. Pat. No.6,685,754 Kindig et al., the disclosures of which are incorporatedherein by reference.

The acetic acid may be vaporized at the reaction temperature, and thenit can be fed along with hydrogen in undiluted state or diluted with arelatively inert carrier gas, such as nitrogen, argon, helium, carbondioxide and the like.

Alternatively, acetic acid in vapor form may be taken directly as crudeproduct from the flash vessel of a methanol carbonylation unit of theclass described in U.S. Pat. No. 6,657,078 of Scates et al., thedisclosure of which is incorporated herein by reference. The crude vaporproduct may be fed directly to the reaction zones of the presentinvention without the need for condensing the acetic acid and light endsor removing water, saving overall processing costs.

Contact or residence time can also vary widely, depending upon suchvariables as amount of acetic acid, catalyst, reactor, temperature andpressure. Typical contact times range from a fraction of a second tomore than several hours when a catalyst system other than a fixed bed isused, with preferred contact times, at least for vapor phase reactions,between about 0.5 and 100 seconds.

Typically, the catalyst is employed in a fixed bed reactor e.g. in theshape of an elongated pipe or tube where the reactants, typically in thevapor form, are passed over or through the catalyst. Other reactors,such as fluid or ebullient bed reactors, can be employed, if desired. Insome instances, it is advantageous to use the hydrogenation catalysts inconjunction with an inert material to regulate the pressure drop, flow,heat balance or other process parameters in the catalyst bed includingthe contact time of the reactant compounds with the catalyst particles.

In one of the preferred embodiments there is also provided a process forselective and direct formation of acetaldehyde from acetic acidcomprising: contacting a feed stream containing acetic acid and hydrogenat an elevated temperature with a suitable hydrogenating catalystcontaining about 0.5 weight percent to about 1 weight percent ofplatinum or ruthenium and about 2.5 weight percent to about 5 weightpercent of tin or iron on a suitable catalyst support. Preferredcatalyst support in this embodiment of the invention is silica.

In this embodiment of the process of this invention, the preferredhydrogenation catalyst contains about 0.5 weight percent or about one(1) weight percent platinum and about five (5) weight percent iron ortin; or about 0.5 weight percent or about one (1) weight percentruthenium and about five (5) weight percent tin or iron. In thisembodiment of the process of this invention, it is preferred that thehydrogenation catalysts are layered in a fixed bed and the reaction iscarried out in the vapor phase using a feed stream of acetic acid andhydrogen in the molar range of about 1:20 to 1:5 and at a temperature inthe range of about 290° C. to 310° C. and at a pressure of reactionzones in the range of about 8 to 20 atmospheres absolute, and thecontact time of reactants is in the range of about 0.5 and 100 seconds.

The following examples describe the procedures used for the preparingvarious catalysts employed in the examples which follow.

EXAMPLE A Preparation of 1 Weight Percent Ruthenium on Iron Oxide

Powdered and meshed iron oxide (99 g) of uniform particle sizedistribution of about 0.2 mm was dried at 120° C. in an oven undernitrogen atmosphere overnight and then cooled to room temperature. Tothis was added a solution of ruthenium nitrosyl nitrate (Heraeus) (3.14g) in distilled water (32 ml). The resulting slurry was dried in an ovengradually heated to 110° C. (>2 hours, 10° C./min). The impregnatedcatalyst mixture was then calcined at 500° C. (6 hours, 1° C./min).

EXAMPLE B Preparation of 3 Weight Percent Ruthenium on Iron Oxide

The procedures of Example A were substantially repeated except forutilizing a solution of ruthenium nitrosyl nitrate (Heraeus) (9.42 g) indistilled water (96 ml) and 97 grams of iron oxide.

EXAMPLE C Preparation of 5 Weight Percent Iron on High Purity, LowSurface Area Silica

Powdered and meshed high purity, low surface area silica (95 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in an oven under nitrogen atmosphere overnight and then cooled to roomtemperature. To this was added a solution of iron nitrate nonahydrate(Alfa Aesar) (36.2 g) in distilled water (36 ml). The resulting slurrywas dried in an oven gradually heated to 110° C. (>2 hours, 10° C./min).The impregnated catalyst mixture was then calcined at 500° C. (6 hours,1° C./min).

EXAMPLE D Preparation of 5 Weight Percent Tin and 0.5 Weight PercentRuthenium on High Purity Low, Surface Area Silica

Powdered and meshed high purity, low surface area silica (94 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in an oven under nitrogen atmosphere overnight and then cooled to roomtemperature. To this was added a solution of tin oxalate (Alfa Aesar)(8.7 g) in dilute nitric acid (1N 45 ml). The resulting slurry was driedin an oven gradually heated to 110° C. (>2 hours, 10° C./min). Theimpregnated catalyst mixture was then calcined at 500° C. (6 hours, 1°C./min). To this calcined and cooled material was added a solution ofruthenium nitrosyl nitrate (Heraeus) (1.57 g) in distilled water (16ml). The resulting slurry was dried in an oven gradually heated to 110°C. (>2 hours, 10° C./min). The impregnated catalyst mixture was thencalcined at 500° C. (6 hours, 1° C./min).

EXAMPLE E Preparation of 1 Weight Percent Ruthenium and 5 Weight PercentIron on High Purity Low, Surface Area Silica

Powdered and meshed high purity low surface area silica (94 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in an oven under nitrogen atmosphere overnight and then cooled to roomtemperature. To this was added a solution of ruthenium nitrosyl nitrate(Heraeus) (3.14 g) in distilled water (32 ml). The resulting slurry wasdried in an oven gradually heated to 110° C. (>2 hours, 10° C./min). Theimpregnated catalyst mixture was then calcined at 500° C. (6 hours, 1°C./min). To this calcined and cooled material was added a solution ofiron nitrate nonahydrate (Alfa Aesar) (36.2 g) in distilled water (36ml). The resulting slurry was dried in an oven gradually heated to 110°C. (>2 hours, 10° C./min). The impregnated catalyst mixture was thencalcined at 500° C. (6 hours, 1° C./min).

EXAMPLE F Preparation of 5 Weight Percent Iron and 1 Weight PercentPlatinum on High Purity, Low Surface Area Silica

Powdered and meshed high purity, low surface area silica (94 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in an oven under nitrogen atmosphere overnight and then cooled to roomtemperature. To this was added a solution of iron nitrate nonahydrate(Alfa Aesar) (36.2 g) in distilled water (36 ml). The resulting slurrywas dried in an oven gradually heated to 110° C. (>2 hours, 10° C./min).The impregnated catalyst mixture was then calcined at 500° C. (6 hours,1° C./min). To this calcined and cooled material was added a solution ofplatinum nitrate (Chempur) (1.64 g) in distilled water (16 ml). Theresulting slurry was dried in an oven gradually heated to 110° C. (>2hours, 10° C./min). The impregnated catalyst mixture was then calcinedat 500° C/ (6 hours, 1° C./min).

EXAMPLE G Preparation of 1 Weight Percent Platinum and 5 Weight PercentTin on High Purity Low Surface Area Silica

Powdered and meshed high purity, low surface area silica (94 g) ofuniform particle size distribution of about 0.2 mm was dried at 120° C.in an oven under nitrogen atmosphere overnight and then cooled to roomtemperature. To this was added a solution of platinum nitrate (Chempur)(1.64 g) in distilled water (16 ml) and a solution of tin oxalate (AlfaAesar) (8.7 g) in dilute nitric acid (1N, 43.5 ml). The resulting slurrywas dried in an oven gradually heated to 110° C. (>2 hours, 10°C./min.). The impregnated catalyst mixture was then calcined at 500° C.(6 hours, 1° C./min).

EXAMPLE H Preparation of 1 Weight Percent Palladium, 1 Weight PercentGold and 5 Weight Percent Potassium Acetate on High Purity, Low SurfaceArea Silica

The procedures of Example D were substantially repeated except forutilizing a solution of palladium nitrate (Heraeus) (2.17 g) indistilled water (22 ml), a solution of gold(III) hydroxide (Alfa Aesar)(1.26 g) and potassium hydroxide (0.28 g) in distilled water (10 ml), asolution of potassium acetate (Sigma) (5 g) in distilled water (10 ml)and 93 grams of silica. The catalyst was sequentially impregnated firstwith palladium and then with gold and finally with potassium acetate.

EXAMPLE I Preparation of 1 Weight Percent Palladium, 5 Weight PercentCopper and 5 Weight Percent Potassium Acetate on High Purity, LowSurface Area Silica

The procedures of Example D were substantially repeated except forutilizing a solution of palladium nitrate (Heraeus) (2.17 g) indistilled water (22 ml), a solution of copper nitrate trihydrate (AlfaAesar) (19 g) in distilled water (20 ml), a solution of potassiumacetate (Sigma) (5 g) in distilled water (10 ml) and 89 grams of silica.The catalyst was sequentially impregnated first with copper and thenwith palladium and finally with potassium acetate.

EXAMPLE J Preparation of 1 Weight Percent Palladium and 5 Weight PercentCopper on Carbon

The procedures of Example D were substantially repeated except forutilizing a solution of palladium nitrate (Heraeus) (2.17 g) indistilled water (22 ml), a solution of copper nitrate trihydrate (AlfaAesar) (19 g) in distilled water (20 ml) and 94 grams of carbon. Thecatalyst was sequentially impregnated first with copper and then withpalladium.

EXAMPLE K Preparation of 1 Weight Percent Palladium and 5 Weight PercentIron on High Purity, Low Surface Area Silica

The procedures of Example D were substantially repeated except forutilizing a solution of palladium nitrate (Heraeus) (2.17 g) indistilled water (22 ml), a solution of iron nitrate nonahydrate (AlfaAesar) (36.2 g) in distilled water (30 ml) and 94 grams of silica. Thecatalyst was sequentially impregnated first with iron and then withpalladium.

EXAMPLE L Preparation of 5 Weight Percent Iron and 5 Weight PercentCobalt on High Purity, Low Surface Area Silica

The procedures of Example D were substantially repeated except forutilizing a solution of iron nitrate nonahydrate (Alfa Aesar) (36.2 g)in distilled water (30 ml), a solution of cobalt nitrate hexahydrate(24.7 g) in distilled water (25 ml) and 90 grams of silica. The catalystwas sequentially impregnated first with iron and then with cobalt.

EXAMPLE M Preparation of 5 Weight Percent Copper and 5 Weight PercentMolybdenum on High Purity, Low Surface Area Silica

The procedures of Example D were substantially repeated except forutilizing a solution of copper nitrate trihydrate (Alfa Aesar) (19 g) indistilled water (20 ml), a solution of ammonium heptamolybdatehexahydrate (Sigma) (9.5 g) in distilled water (65 ml) and 90 grams ofsilica. The catalyst was sequentially impregnated first with copper andthen with molybdenum.

EXAMPLE N Preparation of 5 Weight Percent Tin and 1 Weight PercentRuthenium on High Purity, Low Surface Area Silica

The procedures of Example D were substantially repeated except forutilizing a solution of tin oxalate (Alfa Aesar) (8.7 g) in dilutenitric acid (1N, 43.5 ml), a solution of ruthenium nitrosyl nitrate(Heraeus) (3.14 g) in distilled water (32 ml) and 94 grams of silica.The catalyst was co-impregnated with tin and ruthenium.

EXAMPLE O Preparation of 1 Weight Percent Palladium on Iron Oxide

The procedures of Example D were substantially repeated except forutilizing a solution of palladium nitrate (Heraeus) (2.17 g) indistilled water (22 ml) and 99 grams of iron oxide.

Gas Chromatographic (GC) Analysis of the Products

The analysis of the products was carried out by online GC. A threechannel compact GC equipped with one flame ionization detector (FID) and2 thermal conducting detectors (TCDs) was used to analyze the reactantsand products. The front channel was equipped with an FID and a CP-Sil 5(20 m)+WaxFFap (5 m) column and was used to quantify:

-   -   Acetaldehyde    -   Ethanol    -   Acetone    -   Methyl acetate    -   Vinyl acetate    -   Ethyl acetate    -   Acetic acid    -   Ethylene glycol diacetate    -   Ethylene glycol    -   Ethylidene diacetate    -   Paraldehyde

The middle channel was equipped with a TCD and Porabond Q column and wasused to quantify:

-   -   CO₂    -   Ethylene    -   Ethane

The back channel was equipped with a TCD and Molsieve 5A column and wasused to quantify:

-   -   Helium    -   Hydrogen    -   Nitrogen    -   Methane    -   Carbon monoxide

Prior to reactions, the retention time of the different components wasdetermined by spiking with individual compounds and the GCs werecalibrated either with a calibration gas of known composition or withliquid solutions of known compositions. This allowed the determinationof the response factors for the various components.

EXAMPLE 1

The catalyst utilized was 1 weight percent ruthenium on iron oxideprepared in accordance with the procedure of Example A.

In a tubular reactor made of stainless steel, having an internaldiameter of 30 mm and capable of being raised to a controlledtemperature, there are arranged 50 ml of 1 weight percent rutheniumsupported on iron oxide. The length of the catalyst bed after chargingwas approximately about 70 mm. Prior to the reaction the catalyst wasreduced in situ by heating at a rate of 2° C./min to a final temperatureof 400° C. Then, 5 mol % hydrogen in nitrogen was introduced to thecatalyst chamber at a gas hourly space velocity (GHSV) of 7500 h⁻¹.After reduction, the catalyst was cooled to reaction temperature of 350°C. by continuing the gas flow of 5 mol % hydrogen in nitrogen. Once thereaction temperature was stabilized at 350° C., the hydrogenation ofacetic acid was begun as follows.

A feed liquid was comprised essentially of acetic acid. The reactionfeed liquid was evaporated and charged to the reactor along withhydrogen and helium as a carrier gas with an average combined gas hourlyspace velocity (GHSV) of about 2500 hr⁻¹ at a temperature of about 350°C. The resulting feed stream contained a mole percent of acetic acidfrom about 4.4% to about 13.8% and the mole percent of hydrogen fromabout 14% to about 77%. A portion of the vapor effluent was passedthrough a gas chromatograph for analysis of the contents of theeffluents. The selectivity to acetaldehyde was 60% at a conversion ofacetic acid of 50%.

EXAMPLE 2

The catalyst utilized was 5 weight percent iron on silica prepared inaccordance with the procedure of Example C.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. A portion of the vaporeffluent is passed through a gas chromatograph for analysis of thecontents of the effluents. The acetic acid conversion was 75% andacetaldehyde selectivity was 70%.

EXAMPLE 3

The catalyst utilized was 0.5 weight percent ruthenium and 5 weightpercent tin on silica prepared in accordance with the procedure ofExample D.

The procedure as set forth in Example 1 is substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 4% and acetaldehyde selectivity was 91%. The otherproducts formed were ethane (1%) and ethanol (8%).

EXAMPLE 4

The catalyst utilized was 1 weight percent ruthenium and 5 weightpercent iron on silica prepared in accordance with the procedure ofExample E.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 300° C. A portion of the vaporeffluent is passed through a gas chromatograph for analysis of thecontents of the effluents. The acetic acid conversion is 35% andacetaldehyde selectivity is about 70%.

EXAMPLE 5

The catalyst utilized was 1 weight percent platinum and 5 weight percentiron on High Purity, Low Surface Area Silica prepared in accordance withthe procedure of Example F.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 65% and acetaldehyde selectivity is 60%. The otherproducts formed were carbon dioxide (6%) and ethyl acetate (9%).

EXAMPLE 6

The catalyst utilized was 0.5 weight percent platinum and 5 weightpercent tin on silica prepared in accordance with the procedure ofExample G.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 85% and acetaldehyde selectivity was 65%. The otherproducts formed were methane (4%) and ethyl acetate (9%).

EXAMPLE 7

The catalyst utilized was a commercially available Co/Fe catalystcontaining 17.4 weight percent cobalt and 4.8 weight percent iron onsilica

The procedure as set forth in Example 1 is substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen at atemperature of 350° C. A portion of the vapor effluent is passed througha gas chromatograph for analysis of the contents of the effluents. Theacetic acid conversion is about 65% and acetaldehyde selectivity is 75%.

EXAMPLE 8

The catalyst utilized was 1 weight percent palladium, 1 weight percentgold and 5 weight percent potassium acetate on silica prepared inaccordance with the procedure of Example H.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor lo effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 5% and acetaldehyde selectivity was 98.5%. The otherproducts formed were ethane (1%) and ethanol (0.5%).

EXAMPLE 9

The catalyst utilized was 1 weight percent palladium, 5 weight percentcopper and 5 weight percent potassium acetate on silica prepared inaccordance with the procedure of Example I.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 2% and acetaldehyde selectivity was 97.5%. The otherproduct formed was ethane (2.5%).

EXAMPLE 10

The catalyst utilized was 1 weight percent palladium and 5 weightpercent copper on carbon prepared in accordance with the procedure ofExample J.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the lo effluents. Theacetic acid conversion was 1% and acetaldehyde selectivity was 97%. Theother product formed was ethane (3%).

EXAMPLE 11

The catalyst utilized was 1 weight percent palladium and 5 weightpercent iron on silica prepared in accordance with the procedure ofExample K.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 9% and acetaldehyde selectivity was 96%. The otherproducts formed were ethane (0.6%) and ethanol (3.6%).

EXAMPLE 12

The catalyst utilized was 5 weight percent iron and 5 weight percentcobalt on silica prepared in accordance with the procedure of Example L.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 250° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 11% and acetaldehyde selectivity was 95%. The otherproducts formed were ethane (1%) and ethanol (4%).

EXAMPLE 13

The catalyst utilized was 5 weight percent iron and 5 weight percentcobalt on silica prepared in accordance with the procedure of Example L.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 75% and acetaldehyde selectivity was 70%. The otherproducts formed were methane (4%) and carbon dioxide (3%).

EXAMPLE 14

The catalyst utilized was 5 weight percent copper and 5 weight percentmolybdenum on silica prepared in accordance with the procedure ofExample M.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 10% and acetaldehyde selectivity was 90%. The otherproducts formed were ethane (1.5%) and acetone (6.6%).

EXAMPLE 15

The catalyst utilized was 1 weight percent ruthenium and 5 weightpercent tin on silica prepared in accordance with the procedure ofExample N.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 60% and acetaldehyde selectivity was 78%. The otherproducts formed were methane (6%) and ethanol (12%).

EXAMPLE 16

The catalyst utilized was 1 weight percent palladium on iron oxideprepared in accordance with the procedure of Example O.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 10,000 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of15 bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 66% and acetaldehyde selectivity was 59%. The otherproducts formed were carbon dioxide (4%) and ethanol (18%).

EXAMPLE 17

The catalyst utilized was commercially available copper-aluminumcatalyst sold under the name of T-4489 from Sud Chemie.

The procedure as set forth in Example 1 was substantially repeated withan average combined gas hourly space velocity (GHSV) of 2,500 hr⁻¹ ofthe feed stream of the vaporized acetic acid and hydrogen (H₂ to aceticacid mole ratio of 5) at a temperature of 350° C. and at a pressure of 1bar. A portion of the vapor effluent is passed through a gaschromatograph for analysis of the contents of the effluents. The aceticacid conversion was 88% and acetaldehyde selectivity was 51%. The otherproducts formed were carbon dioxide (5%) and ethanol (16%).

COMPARATIVE EXAMPLES 1A -4A

These examples illustrate the reaction of acetic acid and hydrogen overa variety of catalysts wherein either no acetaldehyde was formed and/orvery low selectivity to acetaldehyde was observed at low conversions ofacetic acid.

In all of these examples, the procedure as set forth in Example 1 wassubstantially followed with the exception of using different catalystsas listed in Table 1. The reaction temperature and selectivity toacetaldehyde and other products are also tabulated in Table 1.

TABLE 1 Acetic Acid Conversion and Selectivities for ComparativeExamples Acetic Ex- Acetaldehyde acid am- selectivity conversion pleCatalyst (%) (%) Other products 1A 5 wt % Cu/ 31 100 ethylene-16%, Fe₂O₃ethane-15%, ethyl acetate-4%, CO₂-5% 2A 5 wt % Co/H- 44 3 ethylene-28%,ZSM-5 ethane-28% 3A 5 wt % Co 5 Wt 78 4 ethylene-14%, % Ru/SiO₂ethane-8% 4A 5 wt % Co/ 0 2 Ethylene-12% Carbon acetone-8%, methane-47%,ethane-5%

While the invention has been illustrated in connection with particularexamples, modifications to these examples within the spirit and scope ofthe invention will be readily apparent to those of skill in the art. Inview of the foregoing discussion, relevant knowledge in the art andreferences discussed above in connection with the Background andDetailed Description, the disclosures of which are all incorporatedherein by reference, further description is deemed unnecessary.

1-31. (canceled)
 32. A process for selective and direct formation ofacetaldehyde from acetic acid comprising: contacting a feed streamcontaining acetic acid and hydrogen at an elevated temperature of up toabout 350° C. with a suitable hydrogenating catalyst carried on asupport chosen from the group consisting of silica, titania, alumina,zirconia, calcium silicate, titania-silica and zirconia-silica, saidhydrogenating catalyst being chosen from the group consisting of: (a)palladium containing catalysts consisting essentially of a combinationof palladium with a second metal chosen from the group consisting ofiron, copper, gold, potassium and combinations thereof; (b) acombination of ruthenium and tin; (c) a combination of copper andmolybdenum; and (d) a combination of iron and cobalt.
 33. The processaccording to claim 32, wherein the catalyst support is selected from thegroup consisting of silica, alumina, silica-alumina, calcium silicate,zirconia, titania and combinations thereof.
 34. The process according toclaim 33, wherein the catalyst support is silica.
 35. The processaccording to claim 33, wherein the hydrogenation catalyst contains acombination of ruthenium and tin at a Ru/Sn weight ratio in the range ofabout 0.1 to
 1. 36. The process according to claim 34, wherein theloading of ruthenium is about 0.5 weight percent to about 1 weightpercent and the loading of tin is about 2.5 weight percent to about 10weight percent and the catalyst support is silica.
 37. The processaccording to claim 35, wherein the loading of ruthenium is about 0.5weight percent and the loading of tin is about 5 weight percent and thecatalyst support is silica.
 38. The process according to claim 32,wherein the hydrogenation catalyst contains a combination of iron andcobalt and wherein the loading level of iron is about 3 weight percentto 10 weight percent and the loading level of cobalt is about 8 weightpercent to about 20 weight percent and the catalysts support is silica.39. The process according to claim 32, wherein the selectivity toacetaldehyde based on acetic acid consumed is at least 60 percent. 40.The process according to claim 32, wherein the selectivity toacetaldehyde based on acetic acid consumed is at least 70 percent. 41.The process according to claim 32, wherein the selectivity toacetaldehyde based on acetic acid consumed is at least 80 percent. 42.The process according to claim 32, wherein the hydrogenation toacetaldehyde is carried out in the vapor phase and at a temperature inthe range of about 250° C. to 350° C.
 43. The process according to claim42, wherein the hydrogenation to acetaldehyde is carried out in thevapor phase and at a temperature in the range of about 270° C. to 310°C.
 44. The process according to claim 42, wherein said feed streamcontains an inert carrier gas.
 45. The process according to claim 42,wherein the reactants consist of acetic acid and hydrogen with a molarratio in the range of about 100:1 to 1:100, the temperature of thereaction zone is in the range of about 250° C. to 350° C., and thepressure of the reaction zone is in the range of about 5 to 25atmospheres absolute.
 46. The process according to claim 42, wherein thereactants consist of acetic acid and hydrogen with a molar ratio in therange of about 1:20 to 1:2, the temperature of the reaction zone is inthe range of about 270° C. to 310° C., and the pressure of the reactionzone is in the range of about 8 to 20 atmospheres absolute.
 47. Aprocess for selective and direct formation of acetaldehyde from aceticacid comprising: contacting a feed stream containing acetic acid andhydrogen at an elevated temperature of up to about 350° C. with asuitable hydrogenating catalyst chosen from the group consisting of: (a)catalysts comprising palladium and gold; (b) catalysts comprisingpalladium and copper; (c) catalysts comprising palladium and iron; and(d) catalysts comprising ruthenium and tin, said catalyst containingabout 0.5 weight percent to about 1 weight percent of palladium orruthenium and 2.5 weight percent to about 5 weight percent of tin oriron on a suitable catalyst support chosen from the group consisting ofsilica, titania, alumina, zirconia, calcium silicate, titania-silica,zirconia-silica and combinations thereof.
 48. The process according toclaim 47, wherein the catalyst contains palladium at a loading level ofabout 0.5 weight percent or about one (1) weight percent and cobalt oriron at a loading level of about five (5) weight percent and thecatalyst support is silica.
 49. The process according to claim 47,wherein the catalyst support contains ruthenium at a loading level ofabout 0.5 weight percent or about one (1) weight percent and tin at aloading level of about five (5) weight percent and the catalyst supportis silica.
 50. The process according to claim 47, wherein the reactantsconsist essentially of acetic acid and hydrogen with a molar ratio inthe range of about 1:20 to 1:5, and the temperature of the reaction zoneis in the range of about 270° C. to 310 °C.
 51. The process according toclaim 47, wherein said catalyst further comprises potassium acetate andthe catalyst support is silica.
 52. A process for selective and directformation of acetaldehyde from acetic acid comprising: contacting a feedstream containing acetic acid and hydrogen at an elevated temperature ofup to about 350° C. with a suitable hydrogenating catalyst chosen fromthe group consisting of: catalysts consisting essentially of palladiumand a second metal chosen from the group consisting of: iron; gold; andcopper, said catalyst containing from about 0.1 weight percent to about1 weight percent of palladium and from about 1 weight percent to about 5weight percent of said second metal on silica.
 53. The process of claim47 wherein said catalyst consists essentially of: palladium and gold ona silica support.
 54. The process of claim 47 wherein said catalystconsists essentially of: palladium and copper on a silica support. 55.The process of claim 47 wherein said catalyst consists essentially of:palladium and iron on a silica support.
 56. The process of claim 47wherein said catalyst consists essentially of: ruthenium and tin on asilica support.